Calculator: Influence of sensor response time (τ 63.2%) on climatic temperature measurements
Copyright© 2019 BARANI DESIGN Technologies s.r.o. Author: Jan Barani τ pronounced "tau" is usually given in seconds and is defined as the amount of time it takes for a meteorological sensor to respond to a rapid change in a measurand. It is very important in measurement of temperature, dew point temperature, humidity and air pressure. Radiosondes are especially affected due to their rapid increase in altitude.
The difference between sensor response time and sensor time constant τ (tau) 63.2% article.
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CALCULATOR INPUTS   Author is the designer of the helical solar radiation shield for precision atmospheric air temperature measurement. Lessons learned during its development include the effects of sensor and shield response time on measurement error as demonstrated in this calculator.
Solar Radiation Shield time constant τ 63.2% (seconds)= Sensor response rate is usually given as τ (tau) 63.2 %. It is a physical property of each sensor.
Temperature sensor time constant τ 63.2% (seconds) =
Fluctuation in
Air temperature (°C) =
You can change the rate of air temperature change with these parameters to see the effect air temperature change has on sensor error and radiation shield error.
Speed of Air Temperature fluctuation (sec) =
Additional Fluctuation in Air temperature (°C) =
Speed of additional True Air Temperature change (sec) =
Time length = Time scale of plot  
10 minute average air temperature measurement error due to slow sensor temperature response and radiation shield airflow restriction  
MEAN temperature measured over 10 minutes MAXIMUM sensor temperature over 10 minutes MINIMUM sensor temperature over 10 minutes RANGE of recorded temperatures over 10 minutes
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ERROR in MEAN temperature reading ERROR in recorded MAXIMUM temperature ERROR in recorded MINIMUM temperature  
Apart from fan-ventilated shields, the helical MeteoShield Professional has the lowest time constant (shortest response time) of any professional solar radiation shield to date.

The advantage of naturally ventilated solar radiation shields over their fan-ventilated counterparts is the fact that they don’t suck in airborne water droplets and dirt onto the internal temperature and humidity sensors.  Fan-aspirated shields in humid, wet and rainy conditions tend to saturate sensors with water to produce unrealistically low air temperature readings during times of morning dew, fog, drizzle, rain and snow. This is due to cooling effects from evaporation. In the short-term, the opposite effect of humid air condensing on metal temperature probes can beneficially temporarily reduce their response time due to heating from water condensation onto the metal surface, but as soon as the probe temperature nears equilibrium with air temperature, the evaporative cooling will overshadow this effect to produce large temperature measurement errors.
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Elapsed Time (seconds) "True" Air Temperature (°C) Solar Radiation Shield internal air temperature (°C) Sensor Temperature Reading (°C) Solar Shield time constant
temperature error contribution (°C)
Temperature Sensor time constant  temperature error contribution (°C) TOTAL Combined air temperature measurement error (°C)  
10min AVERAGE (Mean) =
10min Maximum Value =
10min Minimum Value =
0 sec 0.00 °C 0.00 °C